1) Field of the Disclosure
The disclosure relates generally to composite structures and methods of fabricating the same, and more particularly, to thermoplastic composite tubular structures and methods of fabricating the same using soluble, expandable tooling.
2) Description of Related Art
Thermoplastic and fiber-reinforced thermoplastic composite structures and parts are used in a wide variety of applications, including in the manufacture of aircraft, spacecraft, rotorcraft, watercraft, automobiles, trucks, and other vehicles and structures, due to their high strength-to-weight ratios, corrosion resistance, and other favorable properties. In aircraft manufacturing and assembly, such thermoplastic and fiber-reinforced thermoplastic composite structures and parts are used in increasing quantities to form the fuselage, wings, tail section, skin panels, and other components.
However, the use of thermoplastic composite materials in the design and manufacture of tubular cylindrical and non-cylindrical structures, such as tubes, pipes, ducts, conduits, and elongate hollow components, for use in aircraft, may be difficult due to tooling removal, processing temperature, outer surface dimensional tolerances, fiber alignment, and other processing challenges. Although known methods exist for fabricating tubular cylindrical and non-cylindrical structures, such known methods may use only resin without fiber reinforcement or may use very small fibers, e.g., millimeters long, that are not continuous, and which may be susceptible to decreased interface properties between the fiber and the matrix. Such decreased interface properties may limit the benefits available from higher strength continuous fibers or may result in thermoplastic composite structures that may be susceptible to fatigue.
In addition, known methods exist for fabricating tubular cylindrical and non-cylindrical structures from thermoset composite materials and from aluminum and titanium metal materials. However, the use of thermoset composite materials may require long cure cycles, e.g., 4 hours to 24 hours or more, due to the crosslinking that the thermoset composite materials undergo, and longer cure cycles may result in increased manufacturing time, and in turn, increased manufacturing costs. Further, the use of metal materials may result in increased weight of the aircraft, which, in turn, may result in increased fuel costs during aircraft flight. Moreover, the use of titanium metal materials may result in increased manufacturing costs due to the high cost of such titanium metal materials.
Accordingly, there is a need in the art for improved thermoplastic composite tubular structures and improved methods for fabricating such thermoplastic composite tubular structures that provide advantages over known structures and methods.